EXTERNAL ANATOMY. PBHCHINO FEET. 131 
in their own tribe, they consequently should possess one 
structure in common with the crows. Setting these 
comparatively few exceptions aside, which indicate 
analogical relations, the equality of the toes in the gene- 
rality of insessorial birds, when accompanied with 
slightly curved claws, is a certain indication that such 
birds live habitually upon the ground, and therefore re- 
present either the Grallatorial or the Rasorial type ; 
the birds already mentioned, with hundreds of others, 
places this position beyond dispute. 
(118.) A PERCHiKo FOOT, in the restricted sense in 
which we now use the term, indicates that those birds 
which possess it live more among trees than upon 
the ground. We trace this in the habits of the jays, 
whose inner toes are more or less shorter than the outer 
(Jig. 67 . b). The robin, although so frequently seen upon 
the earth, looking for worms and terrestrial insects, is yet, 
upon the whole, more arboreal ; and we therefore perceive 
that its inner toe is very slightly shorter than the ex- 
ternal one. This disproportion is rather more apparent 
in the stone-chat (Stucicola rubicoki), which, although 
generally considered a more terrestrial bird than the 
robin, we should say, from personal observation, was 
less so ; while in the MotacUla alba, which may be called 
a truly terrestrial bird, the lateral toes are perfectly 
equal. The bush shrikes, both of America and Africa 
(ThamnopbilirM), have the lateral toes very unequal, 
and the claws broad and well curved : this structure is 
in unison widi their manners ; they live only in thickets, 
the intricacies of which they explore in search of insects 
and young or sickly birds. We may therefore define a 
perching foot as of a moderate length, strongly made, 
with the lateral toes unequal, and the hinder one not 
lengthened. This latter character, as we shall presently 
show, being the first indication of a very ditferent type 
of form. 
(119.) Clinging feet are restricted to the humming 
birds, whose structure of foot is perfectly unique. 
From its extreme shortness, on a cursory glance, it 
K 2 
